DALLAS – The Knicks can only wonder what could have been if Kurt Thomas didn’t receive a ridiculous head-butt ejection in the second quarter in his hometown.

The Knicks lost their five-game winning streak but gained some further respect in hanging tough with the Mavericks midway through the fourth quarter at AmericanAirlines Center before collapsing in a 105-90 defeat.

Playing without Thomas, bounced midway through the second period, Stephon Marbury carried the Knicks into contention. But Mavericks rookie Josh Howard proved too much the X-factor and outshined Marbury, who had 24 points and 11 assists.

Howard, an athletic slasher, not only baited Thomas into his untimely dismissal, he wreaked havoc everywhere, scoring a season-high 17 points, snaring eight boards, making four steals and blocking three shots. Dirk Nowitzki, whom Thomas would’ve been on, finished with 27 points.

Thomas was ejected with 6:07 left in the half for a mild head-butt, but it actually was more like a tap. The Knicks had the ball when Thomas was called for an offensive foul away from the play, as he slapped away Howard’s hand that was on him. After the whistle, Thomas moved his head sideways, connecting with Howard’s.

Referee Bennie Adams overreacted, instantly raising his finger for Thomas to leave. Meanwhile, both Howard and Antoine Walker moved at Thomas, trying to get at him, but neither received a technical.

“I was leaning over to talk to him and we hit heads,” Thomas said. “I barely touched him. He didn’t even react. I should have gotten one technical and moved on.”

Thomas, a Dallas native and former Maverick, argued with the officials before leaving the court. He had bought tickets for more than 100 family and friends, spending $6,000. Thomas’ last ejection came during the 2000-01 season, also in Texas, against the Rockets, for cussing a referee. It was the turning point of Thomas’ career; he became much more well-behaved after a tongue-lashing from his mother and sitdown with his agent Jerry Hicks.

A punch is an automatic suspension, but even if the NBA reviews the head-butt today, it’s unlikely Thomas will be suspended for tonight’s pre-All-Star Break finale in New Orleans.

It was a devastating blow for a club giving the Mavericks all they could handle. They held a 27-21 lead in the first quarter when Thomas hit a jumper off a pick-and-roll with Marbury, then the power forward preened on his way downcourt. Who knew his night would end minutes later?

Marbury’s left-wing jumper made it 78-76 with 8:01 left before the Mavs pulled away. A Howard tip-in gave the Mavs a 87-80 lead with 6:10 left. Steve Nash drilled the final dagger, banking in a right-wing 3-pointer with 1:48 left to give them a 100-88 lead.

Lenny Wilkens decided to yank Dikembe Mutombo out of the starting lineup and out of the rotation for the first time because of the Mavericks’ quickness. Even when Thomas was ejected, Mutombo could not get off the pine over starting center Othella Harrington. Michael Doleac started the second half and Mutombo received his first DNP of the season.

Even DerMarr Johnson, the athletic swingman to whom the Knicks are expected to extend another 10-day contract Friday, played ahead of Mutombo. The 7-2 center’s lack of mobility, Wilkens believed, made him vulnerable against the outside-shooting Mavs.